Simple and rapid surface-enhanced Raman Spectroscopy assay for safranine T and its application in highly sensitive determination of mercury (Ⅱ)

A simple and sensitive surface-enhanced Raman spectroscopy (SERS) method for the detection of safranine T (ST) and Hg²⁺ using silver nanoparticles (AgNPs) as substrate was developed. ST can absorb on the surface of AgNPs through electrostatic interaction, the electromagnetic effect combined with chemical adsorption effect give a notable Raman enhancement for ST. The presence of Hg²⁺ well decreased the absorbed ST molecules on AgNPs, leading to a significant decrease of SERS signals thus enabling to detect Hg²⁺. The determination conditions for SERS, including the amount of AgNPs, the concentration of NaCl, the concentration of HCl, the concentration of ST and the reaction time, were optimised. Under the optimised experimental conditions, good linear responses were obtained for ST and Hg²⁺ in the concentration ranges of 0.01–4.0 μmol L^?1 (3.5–1403.4 ng mL^?1) and 0.01–2.0 μmol L^?1 (2.0–401.2 ng mL^?1), the limit of detection were 3.0 nmol L^?1 (1.1 ng mL^?1) and 2.0 nmol L^?1 (0.4 ng mL^?1), respectively. The present method was subsequently applied to the determination of ST in tomato sauces and Hg²⁺ in environmental waters, the recoveries of ST and Hg²⁺ in spiked samples are 95.5–107.8% and 91.4–110.8 %, respectively.     

Electrochemical aptamer sensor for highly sensitive detection of mercury ion with Au/Pt@carbon nanofiber‐modified electrode

In this paper, an electrochemical aptamer sensor was proposed for the highly sensitive detection of mercury ion (Hg²⁺). Carbon nanofiber (CNF) was prepared by electrospinning and high‐temperature carbonization, which was used for the loading of platinum nanoparticles (PtNPs) by the hydrothermal method. The Pt@CNF nanocomposite was modified on the surface of carbon ionic liquid electrode (CILE) to obtain Pt@CNF/CILE, which was further decorated by gold nanoparticles (AuNPs) through electrodeposition to get Au/Pt@CNF/CILE. Self‐assembling of the thiol‐based aptamer was further realized by the formation of Au‐S bond to get an electrochemical aptamer sensor (Aptamer/Au/Pt@CNF/CILE). Due to the specific binding of aptamer probe to Hg²⁺ with the formation of T‐Hg²⁺‐T structure, a highly sensitive quantitative detection of Hg²⁺ could be achieved by recording the changes of current signal after reacting with Hg²⁺ within the concentration range from 1.0 × 10^?15 mol/L to 1.0 × 10^?6 mol/L and the detection limit of 3.33 × 10^?16 mol/L (3σ). Real water samples were successfully analyzed by this method.     

A colorimetric and surface-enhanced Raman scattering dual-signal sensor for Hg based on Bismuthiol II-capped gold nanoparticles

The addition of Bismuthiol II to the gold nanoparticles (AuNPs) solution led to the aggregation of AuNPs with a color change from red to blue. As a result, hot spots were formed and strong surface-enhanced Raman scattering (SERS) signal of Bismuthiol II was observed. However, the Bismuthiol II-induced aggregation of AuNPs could be reversed by Hg²⁺ in the system, accompanied by a remarkable color change from blue to red. As evidenced by UV–vis and SERS spectroscopy, the variation in absorption band and SERS intensity was strongly dependent on the concentration of Hg²⁺, suggesting a colorimetric and SERS dual-signal sensor for Hg²⁺. The sensor had a high sensitivity, low detection limits of 2 nM and 30 nM could be achieved by UV–vis spectroscopy and by SERS spectroscopy, respectively. Other environmentally relevant metal ions did not interfere with the detection of Hg²⁺. The method was successfully applied to detect Hg²⁺ in water samples. It was simple, rapid and cost-effective without any modifying or labeling procedure.     

SERS-based mercury ion detections: principles,strategies and recent advances

Mercury ion (Hg²⁺), known as one of the highly toxic and soluble heavy metal ions, is causing serious environmental pollution and irreversible damage to the health. It is urgent to develop some rapid and ultrasensitive methods for detecting trace mercury ions in the environment especially drink water. Surface-enhanced Raman scattering (SERS) is considered as a novel and powerful optical analysis technique since it has the significant advantages of ultra-sensitivity and high specificity. In recent years, the SERS technique and its application in the detection of Hg²⁺ have become more prevalent and compelling. This review provides an overall survey of the development of SERS-based Hg²⁺ detections and presents a summary relating to the basic principles, detection strategies, recent advances and current challenges of SERS for Hg²⁺ detections.     

Resonance Scattering Detection of Trace Hg2+ Using Aptamer‐modified AuPd Nanoalloy Probe as Catalyst

The 5 nm AuPd nanoalloy in mole ratio of Au:Pd=32:1 was prepared, using sodium citrate as the stabilizing agent and NaBH₄ as the reductant. The AuPd nanoalloy was modified by the aptamer to prepare an aptamer‐ AuPd (AptAuPd) probe for resonance scattering (RS) detection of 5.0–1250 nmol/L Hg²⁺. The AptAuPd‐Hg²⁺ aptamer reaction solution was filtrated by membrane, and the AptAuPd in the filtrate exhibited strong catalytic effect on the slow NiP particle reaction between NiCl₂ and NaH₂PO₂, and the NiP particles showed a RS peak at 508 nm. The RS intensity decreased when Hg²⁺ concentration increased. The decreased RS intensity was linear to Hg²⁺ concentration in the range of 0.5–1250 nmol/L. The RS assays were used to determine Hg²⁺ in real samples, with good results.     

A Highly Sensitive Resonance Scattering Spectral Assay for Hg2+ Based on the Aptamer-Modified AuRu Nanoparticle-NaClO3-NaI-Cationic Surfactant Catalytic Reaction

Gold ruthenium (AuRu) nanoparticles were modified by single strand DNA (ssDNA) to prepare an aptamer AuRu nanoprobe (AuRussDNA) for Hg²⁺. The nanoprobe reacted with Hg²⁺ to form double-stranded T-Hg²⁺-T mismatches, and the released AuRu nanoparticles aggregated to big particles, which induced an increase in the resonance scattering (RS) signal at 592 nm. The RS signal was linear to the concentration of Hg²⁺ in the range of 0.0067–3.3 nmol L^?1. Using the AuRussDNA in filtration solution as a catalyst, a new catalytic RS assay was proposed for detection of trace Hg²⁺. This method was applied for the determination of Hg²⁺ in real samples.     

Facile Fabrication of Multi‐targeted and Stable Biochemical SERS Sensors

The direct transfer of single‐crystalline Au nanowires (NWs) onto Au substrates was achieved by a simple attachment and detachment process. In the presence of a lubricant, Au NWs grown vertically on a sapphire substrate were efficiently moved to an Au substrate through van der Waals interactions. We demonstrate that the transferred Au NWs on the Au substrate can act as sensitive, reproducible, and long‐term‐stable surface‐enhanced Raman scattering (SERS) sensors by detecting human α‐thrombin as well as Pb²⁺ and Hg²⁺ ions. These three biochemically and/or environmentally important analytes were successfully detected with high sensitivity and selectivity by Au NW‐SERS sensors bound by a thrombin‐binding aptamer. Furthermore, the as‐prepared sensors remained in working order after being stored under ambient conditions at room temperature for 80 days. Because Au NWs can be routinely transferred onto Au substrates and because the resultant Au NW‐SERS sensors are highly stable and provide with high sensitivity and reproducibility of detection, these sensors hold potential for practical use in biochemical sensing.     

Dulplex analysis of mercury and silver ions using a label-free fluorescent aptasensor

Label-free Hg²⁺ aptamer was used as a sensing element and the PicoGreen dye was specific to ultra-sensitive double-stranded DNA (dsDNA), which achieved novel fluorescence assay for detection of both mercury and silver ions. In this aptasensor, Hg²⁺ bound to thymidine (T) to form T–Hg^2+-T base pairs and Ag⁺ specifically interacted with C–C mismatches to produce C–Ag⁺–C base pairs. The conformation changes prevented the aptamer from binding to its complementary sequences to form dsDNA and caused a fluorescence intensity decrease with PicoGreen. The change in the fluorescence intensity made it possible to detect both Hg²⁺ and Ag⁺ in a dose-dependent manner. The sensing system could detect as low as 5 × 10^–8 mol/L of Hg²⁺ and 9.3 × 10^–10 mol/L of Ag⁺. The fluorescent intensity changes in the system were specific for Hg²⁺ and Ag⁺, making this simple and cost-effective method extremely valuable in its future applications in monitoring Hg²⁺ and Ag⁺ pollution in environmental analysis.     

Dual recognition strategy for ultra-sensitive fluorescent detection of Hg2+ at femto-molar level based on aptamer functionalized sulfur quantum dots

In the present study, a dual recognition strategy for ultrasensitive detection of Hg²⁺ was successfully developed for the first time based on aptamer functionalized sulfur quantum dots (Apt-SQDs). The developed Apt-SQDs not only retained the good fluorescence properties of quantum dots but also overcame the problem of poor selectivity of SQDs for heavy metal ions. This system used the dual recognition strategy, including the combination of S_x^2? and Hg²⁺ and T-Hg²⁺-T structures to excellently identify and capture Hg²⁺, and an ultrahigh sensitivity fluorescent aptasensor was fabricated. The fluorescent aptasensor had a good response to Hg²⁺ at concentrations ranging of 10^?15 to 10^?7 M with an ultralow limit of detection of 0.3 fM, and the response to other metal ions was far less than that to Hg²⁺. It was successfully applied to detect Hg²⁺ in nearby environmental water samples (tap water, lake water and river water) with a good recovery rate. Moreover, portable test papers that would be useful for Hg²⁺ monitoring in environmental water were designed. The dual recognition strategy not only achieves ultrasensitive fluorescent detection of Hg²⁺ but also provides a new insight into the further expansion of the application of SQDs.     

Aptamer-modified AuRe Nanoalloy Probe for Trace Hg2+ Using Resonance Scattering as Detection Technique

The AuRe nanoalloy particles in molar ratio of 9:1 were prepared by sodium borohydride procedure, and modified by single strand DNA (ssDNA) to prepare an aptamer AuRe nanoprobe (AuRessDNA) for Hg²⁺. In the pH 7.0 Na₂HPO₄‐NaH₂PO₄ buffer solution and in the presence of NaCl, Hg²⁺ interacted with AuRessDNA to form double‐stranded T‐Hg²⁺‐T mismatched and release AuRe nanoparticles that aggregate to large AuRe nanoparticles clusters causing the resonance scattering (RS) peak red shifting and the RS intensity enhanced linearly. On those grounds, 0.067–33.3 nmol·L^?1 Hg²⁺ can be detected rapidly by the aptamer‐modified AuRe nanoparticles RS assay, with a detection limit of 0.04 nmol·L^?1 Hg²⁺. If the aggregated AuRe particles were removed by membrane filtration, the excess AuRessDNA in the filtration solution exhibits catalytic effect on the new Te particle reaction between Na₂TeO₄ and SnCl₂. As the concentration of Hg²⁺ increased, the AuRessDNA nanoparticles in the filtrate solution decreased, the RS intensity at 734 nm decreased linearly. The Hg²⁺ concentration (c) in the range of 0.00133–0.267 nmol·L^?1 was linear to the decreased RS intensity (ΔI_734nm), with a regression equation of ΔI= ?786.4c?4.4, a correlation coefficient of 0.9975, and a detection limit of 0.9 pmol·L^?1 Hg²⁺. This method was applied to the detection of Hg²⁺ in water samples, with satisfactory results.     

Label-free aptamer-based colorimetric detection of mercury ions in aqueous media using unmodified gold nanoparticles as colorimetric probe

We report a simple and sensitive aptamer-based colorimetric detection of mercury ions (Hg²⁺) using unmodified gold nanoparticles as colorimetric probe. It is based on the fact that bare gold nanoparticles interact differently with short single-strand DNA and double-stranded DNA. The anti-Hg²⁺ aptamer is rich in thymine (T) and readily forms T–Hg²⁺–T configuration in the presence of Hg²⁺. By measuring color change or adsorption ratio, the bare gold nanoparticles can effectively differentiate the Hg²⁺-induced conformational change of the aptamer in the presence of a given salt with high concentration. The assay shows a linear response toward Hg²⁺ concentration through a five-decade range of 1 × 10⁻⁴ mol L⁻¹ to 1 × 10⁻⁹ mol L⁻¹. Even with the naked eye, we could identify micromolar Hg²⁺ concentrations within minutes. By using the spectrometric method, the detection limit was improved to the nanomolar range (0.6 nM). The assay shows excellent selectivity for Hg²⁺ over other metal cations including K⁺, Ba²⁺, Ni²⁺, Pb²⁺, Cu²⁺, Cd²⁺, Mg²⁺, Ca²⁺, Zn²⁺, Al³⁺, and Fe³⁺. The major advantages of this Hg²⁺ assay are its water-solubility, simplicity, low cost, visual colorimetry, and high sensitivity. This method provides a potentially useful tool for the Hg²⁺ detection.     

Highly sensitive and selective determination of Hg2+ by using 3-((2-(1H-benzo[d]imidazol-2-yl)phenylimino)methyl)benzene-1,2-diol as fluorescent chemosensor and its application in real water sample

A new receptor 3-((2-(1H-benzo[d]imidazol-2-yl)phenylimino)methyl)benzene-1,2-diol (1) was synthesised and developed as a highly selective fluorescent chemosensor for the detection of Hg²⁺ in semi-aqueous media. The fluorescence of receptor 1 was dramatically and selectively quenched on complexation with Hg²⁺ ion with the detection limit down to 0.20 μM. The developed sensor was successfully applied for the determination of Hg²⁺ content in water samples. Density Functional Theory (DFT) calculations were performed to study the mechanistic behaviour behind the binding of Hg²⁺ with receptor 1.     

Ultrasensitive and rapid screening of mercury(II) ions by dual labeling colorimetric method in aqueous samples and applications in mercury-poisoned animal tissues

Rapid and ultrasensitive detection of trace heavy metal mercury(II) ions (Hg²⁺) are of significant importance due to the induced serious risks for environment and human health. This presented article reports the gold nanoparticle-based dual labeling colorimetric method (Dual-COLO) for ultrasensitive and rapid detection of Hg²⁺ using the specific thymine–Hg²⁺–thymine (T–Hg²⁺–T) as recognition system and the dual labeling strategy for signal amplification. Both qualitative and quantitative detections of Hg²⁺ are achieved successfully in aqueous samples. More importantly, the achieved detection limit of 0.005 ng mL⁻¹ (0.025 nM) without any instruments is very competitive to other rapid detection methods even ICP-MS based methods. This Dual-COLO method is also applied directly for real water sample monitoring and, more importantly, applied in analysis of mercury poisoned animal tissues and body fluidic samples, indicating a potentially powerful and promising tool for environmental monitoring and food safety control.     

A competitive immunoassay for ultrasensitive detection of Hg in water,human serum and urine samples using immunochromatographic test based on surface-enhanced Raman scattering

An immunochromatographic test (ICT) strip was developed for ultrasensitive competitive immunoassay of Hg²⁺. This strategy was achieved by combining the easy-operation and rapidity of ICT with the high sensitivity of surface-enhanced Raman scattering (SERS). Monoclonal antibody (mAb) against Hg²⁺ and Raman active substance 4-mercaptobenzoic acid (MBA) dual labelled gold nanoparticles (GNPs) were prepared as an immunoprobe. The Raman scattering intensity of MBA on the test line of the ICT strip was measured for quantitative determination of Hg²⁺. The ICT was able to directly detect Hg²⁺ without complexing due to the specific recognition of the mAb with Hg²⁺. The IC₅₀ and limit of detection (LOD) of the assay for Hg²⁺ detection were 0.12 ng mL⁻¹ and 0.45 pg mL⁻¹, respectively. There was no cross-reactivity (CR) of the assay with other nineteen ions and the ICT strips could be kept for 5 weeks without loss of activity. The recoveries of the assay for water, human serum and urine samples spiked with Hg²⁺ were in range of 88.3–107.3% with the relative standard deviations (RSD) of 1.5–9.5% (n = 3). The proposed ICT was used for the detection of Hg²⁺ in urine samples collected from Occupational Disease Hospital and the results were confirmed by cold-vapor atomic fluorescence spectroscopy (CV-AFS). The assay exhibited high sensitivity, selectivity, stability, precision and accuracy, demonstrating a promising method for the detection of trace amount of Hg²⁺ in environmental water samples and biological serum and urine samples.     

A novel Hg2+ fluorescence sensor TPE-TSC based on aggregation-induced emission

Abstract

A fluorescent sensor TPE-TSC with aggregation induced emission (AIE) characteristic is synthesized for detecting Hg²⁺ by attaching thiosemicarbazide (TSC) unit into tetraphenylethylene (TPE) group. TPE-TSC exhibits intense green emission in DMSO/H₂O (V:V?=?1:9) solution with the formation of the aggregation. TPE-TSC shows outstanding fluorescence quenching toward Hg²⁺ over other metal ions due to the formation of complex TPE-TSC/Hg²⁺ with a 2:1 binding ratio. The detection limit of TPE-TSC for Hg²⁺ is 1?×?10^?5 mol·L^?1.     

Rhodamine based derivative and its zinc complex: synthesis and recognition behavior toward Hg(II)

A simple fluorescent probe, which contains rhodamine and aminoquinoline moieties, was designed and prepared for selective detection of Hg²⁺ in acetonitrile. RbQ exhibited high selectivity and sensitivity toward Hg²⁺ over other common metal ions. The recognition of RbQ toward Hg²⁺ can be detected by fluorescence spectra, absorption spectra, and even by naked eyes. The binding ratio of the RbQ–Hg²⁺ complex was found to be 1:1 according to Job plot experiment, and the limit of detection was 1.05×10⁻⁷ M. Moreover, the prepared complex RbQ–Zn²⁺ (RbQZ) could detect Hg²⁺ in a ratiometric way and showed lower limit of detection (2.95×10⁻⁸ M) than RbQ in the same condition. Finally, we also demonstrated that the aminoquinoline–zinc complex could be served as a new and effective FRET donor for rhodamine derivatives.     

A novel colorimetric and fluorescent chemosensor: synthesis and selective detection for Cu and Hg

A novel two-channel metal ion sensor has been synthesized from macrocyclic dioxotetraamine and 1,8-naphthalimide derivative. The metal ion-selective signaling behaviors of the sensor were investigated. The sensor presented the selective coloration for Cu²⁺ and Hg²⁺ that can be detected by the naked-eye, respectively. Besides, the addition of Cu²⁺ and Hg²⁺ quenched the fluorescence of 1 obviously and the detection limit was found to be 3 × 10⁻⁷ M for Cu²⁺ and 7 × 10⁻⁷ M for Hg²⁺. This sensor can be utilized for the visual and spectroscopic detection of Cu²⁺ or Hg²⁺ in the presence of the other competing metal ions.     

Dimethylcyclam based fluoroionophore having Hg- and Cd-selective signaling behaviors

Diametrically disubstituted bis(anthrylmethyl) derivative of 1,8-dimethylcyclam exhibited pronounced Hg²⁺- and Cd²⁺-selective fluorogenic behaviors in aqueous acetonitrile solution. A distinctive OFF-ON type signaling was observed for Hg²⁺ and Cd²⁺ ions in aqueous acetonitrile (CH₃CN-H₂O = 90:10, v/v) solution, while a selective ON-OFF type switching behavior toward Hg²⁺ ions was observed in solution having higher water content (CH₃CN-H₂O = 50:50, v/v). The detection limit for the analysis of Hg²⁺ ions in 50% aqueous acetonitrile was found to be 3.8 × 10⁻⁶ M. The selective OR logic gate behavior of the prepared compound toward two toxic heavy metal ions of Hg²⁺ and Cd²⁺ ions in CH₃CN-H₂O (90:10, v/v) suggests the possibility as a new chemosensing device for the two important target metal ions.     

Characterization of a Hg2+-Selective Fluorescent Probe Based on Rhodamine B and Its Imaging in Living Cells

A small organic molecule P was synthesized and characterized as a fluorometric and colorimetric dual-modal probe for Hg²⁺. The sensing characteristics of the proposed probe for Hg²⁺ were studied in detail. A fluorescent enhancing property at 583 nm (>30 fold) accompanied with a visible colorimetric change, from colorless to pink, was observed with the addition of Hg²⁺ to P in an ethanol-water solution (8:2, v/v, 20 mM HEPES, pH 7.0), which would be helpful to fabricate Hg²⁺-selective probes with “naked-eye” and fluorescent detection. Meanwhile, cellular experimental results demonstrated its low cytotoxicity and good biocompatibility, and the application of P for imaging of Hg²⁺ in living cells was satisfactory.     

Hg-selective fluoroionophoric behavior of pyrene appended diazatetrathia-crown ether

Bis(pyrene) derivative of diazatetrathia-crown ether has been prepared and its Hg²⁺-selective fluoroionophoric properties were investigated. The compound showed a pronounced Hg²⁺-selectivity and other metal ions except for Cu²⁺ showed almost no discernible responses. The Hg²⁺-selectivity of the compound was also confirmed by the competitive experiments performed in the presence of physiologically important metal ions and the detection limit was found to be 1.6 × 10⁻⁶ M. The prominent selective and efficient fluorescence quenching behavior could be utilized as a new chemosensing system for the analysis of toxic Hg²⁺ ions in aqueous environment.